Synthesis of different immunotoxins composed by ribosome inactivating proteins non-covalently bound to monoclonal antibody.

This study describes the synthesis of a panel of immunotoxins made by a non-covalent interaction between a monoclonal antibody derivatized with a dichlorotriazinic dye and six different ribosomal inhibitor proteins: colocin 1, momorcochin, momordin, bryodin, saporin 6 and PAP-S. The scheme of preparation showed several advantages respect to commercially available heterobifunctional cross-linkers, such as an higher overall yield of production and the homogeneity of the obtained conjugates. Nevertheless this procedure allowed the synthesis of immunoconjugates only for the four glycosilated RIPs since the not glycosilated ones saporin 6 and PAP-S precipitated in the presence of the dye. The non covalent linkage did not significantly affect the toxic activity of the glycosilated RIPs, as shown by their antitumoral activity on three different cell lines: HT-29 and A431 as target and MeWo as control. Furthermore, the monoclonal antibody cell-antigen recognition was preserved if a maximum derivatization ratio of 4 between the antibody and the dye was applied. The described original procedure may be of general application to prepare panels of immunotoxin for clinical use avoiding the expected RIP-related immune reaction.